Maria Apostolopoulou

The growing penetration of renewable energy sources has intensified the demand for safe, sustainable, and cost-effective energy-storage technologies. Aqueous lithium-ion batteries are promising candidates because of their intrinsic safety and high ionic conductivity, though their deployment is limited by narrow electrochemical stability window of water. Lithium titanate oxide (LTO) has emerged as an ideal anode material for aqueous systems because of its exceptional structural stability, negligible volume change during lithiation/delithiation, and relatively high operating potential that suppresses hydrogen evolution. This review examines the peer-reviewed literature (2010–2026) on LTO-based aqueous lithium-ion batteries, focusing on the interdependence between material synthesis, electrode fabrication, electrolyte engineering, and electrochemical performance. Scalable fabrication techniques, such as spray deposition and tape casting, are discussed alongside their pact on electrode quality. Attention is given to water-in-salt, gel-polymer, and localized high-concentration electrolytes that expand the stability window and improve interfacial behavior. Overall, the review highlights how electrolyte design, electrode architecture, and processing methods can be jointly tailored to support stable and scalable LTO-based aqueous lithium-ion batteries systems.

Conventional carbon-based electrodes like graphene are limited by costly, energy-intensive synthesis that rely on non-renewable precursors, challenging their scalability. While biomass-derived carbons (biochar) are a promising green alternative, achieving state-of-the-art performance typically requires chemical activation. Developing high-performance biochar through simple, scalable, and green pathways therefore remains a key challenge. In this work, we present a comprehensive physicochemical characterization of activation-free biochar derived from walnut, carob, rice husk and coffee via simple pyrolysis. Surface area, porosity and structural disorder were systematically analyzed to identify the key parameters governing ion interaction and charge storage. The results reveal a strong dependence of biochar properties on biomass type, with pronounced differences in accessible porosity and defect density. Among the materials studied, walnut-derived biochar combined a high specific surface area (1146 m²/g) with a high degree of structural disorder, highlighting the critical role of defects in enhancing ion adsorption and charge-transfer processes. Electrochemical measurements illustrated the functional implications of these intrinsic characteristics. Overall, this work demonstrates that carefully selected, unprocessed biomass can serve as a direct, low-cost source of functional carbon electrodes, providing insight into the parameters that dictate their electrochemical behavior and enable broader functional potential.

Lithium-ion batteries, due to their high energy density, compact size, long lifetime, and low environmental impact, have achieved a dominant position in everyday life. These attributes have made them the preferred choice for powering portable devices such as laptops and smartphones, power tools, and electric vehicles. As technology advances rapidly, the demand for even more efficient energy storage devices continues to rise. In lithium-ion batteries, anodes play a crucial role, with lithium titanate oxide standing out as a highly promising material. This anode is favored for its exceptional cycle stability, safety features, and fast charging capabilities. The impressive cycle stability of lithium titanate oxide is largely due to its zero-strain nature, meaning it undergoes minimal volume changes during lithium-ion insertion and extraction. This stability enhances the anode’s durability, leading to longer battery life. In addition, the lithium titanate oxide anode operates at a voltage of approximately 1.55 V vs. Li⁺/Li, significantly reducing the risk of dendrite formation, a major safety concern that can cause short circuits and fires. The material’s spinel structure, with its large active surface area, further allows fast electron transfer and ion diffusion, facilitating fast charging. This review explores the characteristics of lithium titanate oxide, the various synthesis methods employed, and its integration with carbon materials to enhance cycle stability, coulombic efficiency, and safety. It also proposes strategies for optimizing lithium titanate oxide properties to create sustainable anodes with reduced environmental impact using eco-friendly routes.